1. Field of the Invention
The present invention relates to an integrated hybrid circuit applied to a digital subscriber loop and a setting method thereof, and particularly to an integrated hybrid circuit applied to a digital subscriber loop and a setting method thereof that not only can increase an upstream rate, but can also efficiently reduce echo noise coupled to a receiving circuit of the integrated hybrid circuit from a transmission unit of the integrated hybrid circuit.
2. Description of the Prior Art
Please refer to FIG. 1. FIG. 1 is a diagram illustrating an integrated hybrid circuit 100 applied to a digital subscriber loop according to the prior art. As shown in FIG. 1, after a transmission driver 102 receives a user transmission signal US, the transmission driver 102 can generate a pair of upstream signals. Coils 1042, 1044 of a transceiver circuit 104 receives and couples the pair of upstream signals to a transceiver coil 106. Then, the transceiver coil 106 transmits the pair of upstream signals to a central office 110 through a twisted pair 108. On the other hand, the transceiver coil 106 receives a pair of downstream signals from the central office 110 through the twisted pair 108 and couples the pair of downstream signals to the coils 1042, 1044. Then, the pair of downstream signals is transmitted to a receiving terminal 112 through the coils 1042, 1044. As shown in FIG. 1, the integrated hybrid circuit 100 utilizes a four-to-two transceiver circuit to implement a full-duplex technology to increase efficiency of the hybrid circuit 100. But, a disadvantage of the full-duplex technology is that the receiving terminal 112 of the integrated hybrid circuit 100 may receive coupling noise coupled from the pair of upstream signals, that is, echo noise coupled from the pair of upstream signals. As shown in FIG. 1, matching circuits 114, 116 are used for matching output impedances of the coils 1042, 1044 to decrease echo noise coupled to the receiving terminal 112 from the pair of upstream signals, where the output impedances include impedances of the digital subscriber loop. Although the matching circuits 114, 116 can be designed to have variable impedances, echo cancellation capability of the matching circuits 114, 116 maybe not good because the priori art does not consider transmission power of the transmission driver 102 of the hybrid circuit 100, bandwidth of a filter of the transmission driver 102 of the hybrid circuit 100, bandwidth of a filter of the receiving terminal 112 of the integrated hybrid circuit 100, an upstream rate, and a downstream rate, resulting in the upstream rate and the downstream rate not being optimized.
FIG. 5 is a diagram illustrating a hybrid circuit applied to a digital subscriber loop according to another priori art (as shown in FIG. 2 of U.S. Pat. No. 6,931,122B2), which adds a matching circuit 201 to increase echo noise suppression capability. However, it still could not tune matching impedance contained in the matching circuit 201 according to subscriber loop length and types, neither to reduce echo noise and increase upstream rate by tuning bandwidth and power of filter at transmission side, and bandwidth of filter at receiving path.